I see a lot of prisons where visitation is not at a visitor table but one on one through a window. It seems like it would help get rid of all that contraband, but I do not seem to have the option (the only "visitor" item is the visitor table).
This is a different item called a Visitation Booth. It is placed in visitation rooms like tables, but it is accessed through the Utilities menu rather than the Objects menu. they are usually placed in a line that splits the visitation room in two. One side (the visitor side, with 3 seats) can lead back to your reception or to the prison entrance, while the other side (prisoner side, with one seat) leads back into the prison. In this way you can keep your visitors and prisoners separate, and there is no way for prisoners to escape through the visitation room.